Sound suppressors particularly for jet engines



Oct. 31, 1967 G. KURTZE 3,349,868

SOUND SUPPRESSORS PARTICULARLY FOR JET ENGINES Filed NOV. 9, 1964 3 Sheets-Sheet 1 GIJ/WER Kw? 725 By flwuw A wk,

Arm/MY G. KURTZE Oct. 31, 1967 SOUND SUPPRESSORS PARTICULARLY FOR JET ENGINES 1964 5 Sheets-Sheet 2 Filed Nov. 9,

mm Gun/r52 16012726 By I l/dud AND/INF) Oct. 31, 1967 G. KURTZE 3,349,868

SOUND SUPPRESSORS PARTICULARLY FOR JET ENGINES Filed Nov. 9, 1964 3 Sheets-Sheet 3 United States. Patent Ofitice 3,349,868 Patented Oct. 31 1967 Germany Filed Nov. 9, 1964, Ser. No. 409,645

application Germany, Nov. 8, 1963,

Claims priority,

G 13 Claims. (51. 181-51) The present invention relates to sound suppressors which are particularly adapted to suppress the sound of jet engines. As is well known, it is necessary when testing jet engines for maintenance purposes to operate these engines while the aircraft is grounded, and because of the extremely loud noise resulting from the operation of the jet engine it is essential that sound suppressors be used in order to suppress this noise, particularly in certain areas where people live at relatively short distances from an airport or the like where the maintenance on the jet engines is carried out. In fact, certain localities have laws which require suppression of this noise.

It is a primary object of the present invention to provide a sound suppressor which avoids the disadvantages existing in hitherto known devices of this type.

Thus, it is one of the objects of the present invention to provide a sound suppressor which is capable of efiiciently handling even relatively low frequencies.

Furthermore, it is an object of the present invention to provide a sound suppressor which will maintain the structure of the suppressor at a temperature sufiiciently low to prevent any damage to the suppressor while at the same time avoiding the use of structures such as tubular grids or the like which must themselves be intensively cooled in order to be protected from the high temperatures. Such grids also act to convert the low frequency sound vibrations into high frequency vibrations, and since the structure of the invention can efficiently handle sounds of low frequency, it is unnecessary to provide a grid for this purpose either.

In addition it is an object of the present invention to provide a structure which will very reliably guide to the exterior of the sound suppressor the heat waves which would tend to subject the components of the sound suppressor, particularly its curved parts, to excessive temperatures, while at the same time directing a relatively large portion of the sound energy along the interior of the sound suppressor.

Furthermore, it is an object of the present invention to provide a sound suppressor of relatively small cross sectional area without risking the danger of too great a drop in pressure.

Furthermore, it is an object of the present invention to provide a sound suppressor which can overlap the discharge end of the jet engine to a considerable extent so that it reliably avoids the escape of the discharge gases forwardly without passing through the sound suppressor. However, with the invention the inlet end of the sound suppressor need not be very accurately adjusted with respect to the jet engine, and in particular changes in the elevation of the nozzle at the discharge end of the jet engine during operation thereof have absolutely no influence on the sound suppressor of the invention within certain limits.

Furthermore, it is an object of the invention to provide a sound suppressor which is composed of a relatively small number of simple elements which are easily assembled.

In addition, it is an object of the present invention to provide a sound suppressor whose components can easily be collapsed so that when the sound suppressor is not in use it will occupy extremely small amount of space so that it can easily be transported or stored.

In addition, it is an object of the invention to provide a sound suppressor with components which are adjustable with respect to each other and with respect to a jet engine so as to be capable of being placed in the best possible condition for achieving the desired results.

With the above objects in view the invention includes, in a sound suppressor for jet engines or the like, an elongated substantially horizontal channel having an upper portion which is open to the outer atmosphere over most this channel having an open inlet end gases directly from the discharge of a jet engine or the like. Because of the fact that the soundsuppressing channel of the invention is open to the outer atmosphere at an upper portion of the channel throughout most of the length of the channel, it is possible to achieve many of the advantages referred to above, as will be apparent from the description below.

best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a perspective illustration of one possible embodiment of a sound suppressor according to the invention;

FIG. 1a is a perspective illustration sor similar to FIG. shown in FIG. 1;

FIG. 2 shows in a longitudinal sectional view the structure in the interior of a sound suppressor of the invention;

FIG. 3 is a top plan view of the sound suppressor of FIG. 2;

FIG. 3a is a top plan view of another embodiment of a sound suppressor according to the invention;

FIG. 4 is a perspective view of a collapsible sound suppressor of the invention; and

FIG. 5 shows yet another embodiment of a sound suppressor, in a longitudinal sectional view.

Referring now to the drawings, it will be seen from FIG. 1 that the elongated suppressor of the invention is in the form of a substantially horizontal channel 1 which has an upper portion which is open to the outer atmosphere over substantially the entire length of the channel. The elongated sound suppressor shown in FIG. 1 sound-absorbing material. As may be seen from FIG. 1 the sound suppressor which of a sound suppresalong its entire upper portion, tial that it be opened to the outer atmosphere over the major part of its upper portion, has a pair of side walls 3 which are fixed to and extend upwardly from a bottom wall 2 which thus serves also to interconnect the side walls 3. If desired, elongated connecting bars can extend between and be connencted to the side walls 3, and such connecting bars 2a are shown in FIG. la, FIG. 2, and in FIG. 3a. The side walls 3 are each preferably composed of a pair of shells which are spaced from each other to define with respect to each other a space which may be filled with sound-absorbing material. Thus, as may be seen from FIG. 1, each side wall 3 includes an outer shell 3a and a perforated inner shell 3b, and the space between these shells is filled with the sound-absorbing material. The side walls can be completely fiat, and can extend parallel to the direction of flow of the stream issuing from the jet engine, although, if desired the side walls can diverge or converge slightly away from or toward each other, respectively, in the direction of flow of the discharge gases from the jet engine. Also, it is possible for the side walls to be inclined toward each other adja- 3% cent their upper edge portions, as is apparent from FIG. 1 where such inclined portions 3 of the side walls 3 are illustrated, the portions of the side walls 3 which are situated beneath their upper portions 3 extending vertically and being of course parallel to each other.

The height H of each side wall 3 is preferably equal to or greater than five times the diameter of the discharge nozzle, while the distance A between the side walls is equal to or greater than three times the diameter of the discharge nozzle of the jet engine which is placed with its discharge nozzle communicating with the inlet end of the sound suppressor of the invention during testing and checking of the jet engine. The inlet end of the sound suppressor of FIG. 1 is shown at the left of FIG. 1, and at its end distant from its inlet end the sound suppressor has a curved portion 4 which directs the gases upwardly and out of the sound suppressor to the outer atmosphere.

As may be seen from FIG. 2, the sound suppressor illustrated therein supply rests directly on the supporting surface 7, which may be the ground, and this sound suppressor has the reinforcing cross bars 2a and the side walls 3 extend straight up to their very top edges so that they do not have portions 3 inclined toward each other. However, the right end of the sound suppressor of FIG. 2 is identical with the right end of the sound suppressor of FIG. 1, and at this end of the sound suppressor which is distant from the inlet end thereof not only is the bottom wall of the sound suppressor curved upwardly to the top of the sound suppressor, as indiciated at the right ends of FIGS. 1 and 2, but in addition the sound suppressor can carry baffles 4a extending between and fixed to the side walls 3 so as to further reinforce the side walls while at the same time contributing to the reflecting of the stream upwardly and out of the sound suppressor at its end distant from the jet engine.

In order to render the sound suppressor of the invention easily transportable it can be carried by wheels such as the wheels 5 shown in FIG. 1, or any suitable carriage structure can be used to support the sound suppressor while rendering it easily transportable. However, in FIG. 2, as was pointed out above, the structure rests directly on the ground or other supporting surface so that it is not essential for the structure of the invention to be mobile.

FIG. 2 shows how the jet engines 6 at the tail assembly of the aircraft extend into the sound suppressor, and of course it is highly desirable to provide an arrangement where these jet engines can extend through a considerable distance into the sound suppressor so as to prevent as much as possible escape of gases forwardly from the sound suppressor without passing therethrough. Inasmuch as the sound suppressor of the invention is completely open at its upper portion it is simple to receive the tail assembly in the interior of the suppressor in the manner shown in FIG. 2.

The reinforcing and stabilizing or stiffening of the side walls is of course provided by the transverse bars 2a as well as by the baflies 4a. For this purpose the reinforcing bars 2a are located at suitable parts of the assembly. With an arrangement as shown in FIG. 2, it is possible to eliminate a bottom plate such as the bottom wall 2 and to use instead the floor 7 for this purpose, and in this case the side walls 3 and the deflecting portion 4 will be directly built into or anchored to the floor support 7.

FIG. 3 shows the construction of FIG. 2 in a top plan view, and it is apparent from FIG. 3 that the sound suppressor can be used for several jet engines 6 which can be operated simultaneously. However, in accordance with the invention care should be taken to see to it that the free distance A between a side wall 3 and the adjoining outlet of the nearest jet engine is equal to or greater than the diameter of the outlet of the jet engine so that in this way failure to mix the hot gases with sufficient fresh air can be avoided and thus the walls of the sound suppressor, and in particular the sound-absorbing material carried thereby, can be reliably protected from the hot gases. On the other hand, the distance A, for acoustical reasons, should not be too great. In order to be able to adapt the sound suppressor of the invention to all types of engines, the sound suppressor is constructed in accordance with the invention so that the distance between the side walls can be adjusted. For this purpose one of the side walls can be mounted in any well known manner so as to be movable toward and away from the other of the side walls to permit adjustment of the distance A and thus adapt the structure to a particular engine. Of course, both side walls can be made movable, if desired.

A particularly preferred form of the invention is illustrated in FIG. 3a which, in the same way as FIG. 3, shows the construction in a top plan view. In order to be able to adapt the side walls 3 to a particular jet engine 6, such as that indicated in FIG. 3a, each of the side walls is provided at its forward end with a turnable flap portion 3c pivotally connected to the remainder of the side wall by a vertically extending hinge, so that in this way each forward portion 30 is turnable in the direction indicated by the arrows 8, and any suitable structure may be provided for releasably maintaining these turnable front flap portions of the side walls at selected angular positions, so that the structure of the invention can be adjusted at its inlet end so as to be adapted to a particular jet engine. Of course, while both of the side walls 3 have turnable front flap portions 3c, as indicated in FIG. 3a, and certainly this construction is preferred because it maintains the symmetry of the arrangement, nevertheless it is possible to provide only one of the side walls with a turnable front flap portion 3c, and still it will be possible to adapt the structure to a particular jet engine or a plurality of jet engines.

Thus, it is possible to adjust the structure of the invention in an extremely short time so that it will be properly adapted to the particular requirements of a particular engine or engines, as in the case of FIG. 3. It will be noted that in FIG. 3 the rear curved end portion 4 as well as the baffles 4a are provided, FIG. 3 being a top plan view of FIG. 2, while in FIG. 3a these latter elements are omitted, and in fact FIG. 1a shows a sound suppressor which has an open rear end distant from its inlet end and including no curved portions or baffles or the like. This structure will also operate reliably to produce the desired results even though the stream is not deflected upwardly at the discharge end of the sound suppressor.

In order to be able to situate the sound suppressor under conditions where it is being transported or stored in the smallest amount ofspace, the side walls thereof, in particularly, are made collapsible, as indicated in FIG. 4 where according to a preferred embodiment of the invention each side wall 3 is made up a plurality of longitudinal sections 3, 3", 3 and 3"" which are hingedly connected to each other by hinges 3a so that each wall can be moved between the solid collapsed condition shown in FIG. 4 and the dotted raised position. Thus, a quick placing of the collapsed assembly in its mounted condition ready for operation is possible, and of course the same is true of the collapsing of the assembly. Any suitable lock devices (not shown) can be provided for releasably maintaining the sections of the structure in their desired relative positions in the collapsed and mounted conditions. In the example shown in FIG. 4 the rear portion 4 also is connected with the base by a hinge 4a so that it can be. turned from the solid to the dotted position shown in FIG. 4 after which the side walls 3 can be raised and suitably arrested relative to one another as stated before.

Thus, it is possible with an extremely simple construction to provide a sound suppressor which can be adapted to all types of engines and operating conditions and which at the same time is extremely light and easy to move about and manipulate.

Referring now to FIG. 5, the sound suppressor 1 illustrated therein includes a pair of side walls 3 identical with the side walls 3 described above. The tail assembly and jet engines 6 of an aircraft are situated at the inlet endla of the suppressor as indicated in FIG. 5. In ac cordance with the present invention, the sound suppressor of FIG. 5 includes a gas-guiding means formed by the curved unit in the form of an elongated channel having a curved top wall extending through substantially 90 and curved as illustrated in FIG. 5, this channel including side walls which extend downwardly and preferably perpendicular to the wall shown in section in FIG. 5, and the edges of the side walls distant from the transverse upper wall of this channel 10 are completely unconnected from each other so that the channel is completely open at its bottom, as viewed in FIG. 5. The channel or gas-guiding means 10 will operate according to the well known Coanda effect, according to which the gas issuing from the jet engine 6 will cling to the convex inner surface of the transverse -wall 10 so that in this way the gaseous stream 14 will be deflected upwardly and out of the suppressor as indicated in FIG. 5. On the other hand, the sound waves will not be influenced by the Coanda effect and thus will not curve upwardly and outwardly with the gas stream 14. Instead the sound waves 15 will for the most part continue to travel along the interior of the suppressor which in the example illustrated in FIG. 5 rests with its bottom wall 2 on the floor 7.

As may be seen from FIG. 5, the end of the suppressor of this embodiment is closed by an end wall 11 which may have its surface 12, which is directed toward the interior of the suppressor, extending at any desired angle, with respect to the floor 7. Thus, either the end wall 11 or at least its inner surface 12 can be plane, and vertical, or at any desired angle with respect to the bottom support 7. Also, the inner surface 12 preferably carries sound-absorbing means such as the illustrated sounddeadening wedge elements 13 fixed to and projecting from the surface 12, although any other sound-absorbing medium of high efiiciency can be used.

It is to be noted that in all of the embodiments of the invention because the elongated sound-suppressing channel is open at its upper portion throughout a major part of the suppressor of the invention the exterior air has free access to the interior of the sound suppressor so that an intensive cooling of the stream issuing from the jet engine can take place through this free communication between the interior of the sound suppressor with the outer atmosphere. However, it is to be noted that with the embodiment of FIG. 5 the deflection of the hot gaseous stream out of the sound suppressor with the gasguiding means 10 which works according to the Coanda effect will very reliably prevent any unusually high temperatures from prevailing in the interior of the sound suppressor. As is well known the Coanda effect recognizes the fact that a gas stream will hug and flow along a convexly curved guide surface such as the inner convex surface of the transverse wall of the guide means 12.

Furthermore, it will be noted that with the arrangement of FIG. 5 the sound energy for the most part does not go out to the exterior and instead flows as indicated by the arrow 15 along the lower part of the suppressor toward its end wall 11 so that the sound is very greatly suppressed directly in the interior of the suppressor of FIG. 5.

With the gas guiding means 10, even though the gaseous stream is guided out as indicated by the arrows 14 by the Coanda effect, the innermost part of the gas stream, wherethe highest temperatures prevail, never comes into contact with any of the structure of the invention. Moreover, because of the streaming of the gas in the manner shown in FIG. 5 fresh air is sucked along with the gas to surround the gaseous stream and the guide means 10 so as to protect the latter from overheating, and thus it is possible to use for the structure of the invention very few components made of special heat-resistant material, and instead conventional materials can be used for the most part.

As a result of the fact that the elongated channel of the invention is open to the outer atmosphere at the upper part of the channel throughout most of the length thereof, it is possible, without any substantial increase in the admission of the sound energy to the outer atmosphere, to sharply localize the sound waves even at low frequencies and to direct them upwardly into the atmosphere.

As was indicated above, it is possible to provide the structure of the invention with a relatively small cross sectional area without risking the danger of too great of a drop in pressure, because the stream of gases can freely expand upwardly. Thus, baffles such as those shown in some of the embodiments at 4 and 4a are not absolutely essential, because with the instruction of the invention even if the gas flows only horizontally it will leave the suppressor of the invention at a speed which is less than meters per second.

Also, because of the fact that the suppressor of the invention is open at its top the adjustment in elevation with respect to a jet engine need not be very accurately carried out and within certain limits there is a complete freedom in elevation in the relative positions between the jet engine and the suppressor.

By making the side walls 3 of a height which is equal to or greater than five times the diameter of the discharge nozzle of the jet engine, as pointed out above, the extent of sound reduction provided by the side walls will be at least 15 decibels, and this extent of sound reduction in itself corresponds to the performance which can be expected of conventional mobile sound suppressors.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of sound suppressors differing from the types described above.

While the invention has been illustrated and described as embodied in sound suppressors to be used with jet engines, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for Various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a sound suppressing arrangement wherein a jet engine has an outlet of a given diameter situated in close proximity to an inlet end of an elongated substantially horizontal channel adapted to receive gases discharged from the outlet and having an upper portion which is open to the outer atmosphere along at least a major part of said channel, the improvement comprising guide means arranged in said channel and including at least one guide member which curves from the interior to the exterior of said channel for directing the gases out of the channel.

2. In a sound suppressing arrangement as defined in claim 1, wherein said channel comprises opposed side walls, each having a height at least five times that of the given diameter of said outlet of said jet engine, and said side walls being transversely spaced from each other by a distance at least three times that of such given diameter.

3. In a sound suppressing arrangement as defined in claim 1, wherein said channel comprises opposed side Walls each having 'a given height and being spaced from one another by a minimum distance constituting a fraction of said given height; and means mounting at least one of said walls movable with reference to the other for increasing said distance.

4. In a sound suppressor for jet engines or the like, in combination, an elongated channel having an open inlet end for receiving gases directly from the outlet of a jet engine, said channel extending substantially horizontally and having an upper portion which is open to the outer atmosphere along substantially the entire length of said channel, said channel having in its exterior an outwardly curved gas guiding means which curves from the interior to the exterior of said channel.

5. In a sound suppressor as defined in claim 4, wherein each said channel comprises spaced opposite side walls each including a portion adjacent said inlet end and pivotally connected to the remainder of the respective side wall for movement about an axis substantially normal to the direction of elongation of said channel, so that the respective portions can be turned toward and away from each other to thereby adapt the inlet end of said channel to the configuration of different jet engine outlets.

6. In a sound suppressor as defined in claim 4, wherein said channel has a terminal end spaced from said inlet end; and further comprising wall means extending transversely of the direction of elongation of said channel at said terminal end at least substantially closing the latter.

7. In a sound suppressor as defined in claim 6, wherein said guide means is arranged intermediate said inlet and terminal ends spaced from said wall means.

8. In a sound suppressor as defined in claim 6, wherein said wall means has a surface facing the interior of said channel and extending substantially normal to the direction of elongation of the same.

9. In a sound suppressor as defined in claim 6, wherein said wall means has a surface facing the interior of said channel and defining an acute angle with the direction of elongation of the same.

10. In a sound suppressor as defined in claim 6, wherein said Wall means has a surface facing the interior of said channel; and further comprising sound-absorbing means provided on said surface.

11. In a sound suppressor for jet engines or the like, in combination, an elongated substantially horizontal channel having an inlet end for receiving gases directly from the outlet of a jet engine and having distant from said inlet end an end wall extending across and closing said channel, said channel having an upper portion which is open to the outer atmosphere along substantially the entire length of said channel, and said channel carrying in its interior a gas-guiding means which curves from the interior to the exterior of the channel and which guides gases outwardly of said channel according to the Coanda eiiect.

12;. In a sound suppressor as recited in claim 11, said end wall carrying sound-absorbing means directed toward the interior of the channel.

13. In a sound suppressor as recited in claim 12, said sound-absorbing means including a plurality of sounddeadening wedge members.

References Cited UNITED STATES PATENTS 2,608,363 8/1952 Shumaker 181-33 2,936,040 5/ 1960 Rennard 181-33 3,011,584 12/1961 Lemmerman et al. 181-33 3,014,410 12/1961 Anderson 18l-33 FOREIGN PATENTS 1,128,475 8/ 1956 France.

774,550 5/1957 Great Britain.

847,482 9/ 1960 Great Britain.

865,421 4/1961 Great Britain.

890,106 2/ 1962 Great Britain.

RICHARD B. WILKINSON, Primary Examiner. ROBERT S. WARD, JR.,Exa miner. 

1. IN A SOUND SUPPRESSING ARRANGEMENT WHEREIN A JET ENGINE HAS AN OUTLET OF A GIVEN DIAMETER SITUATED IN CLOSE PROXIMITY TO AN INLET END OF AN ELONGATED SUBSTANTIALLY HORIZONTAL CHANNEL ADAPTED TO RECEIVE GASES DISCHARGED FROM THE OUTLET AND HAVING AN UPPER PORTION WHICH IS OPEN TO THE OUTER ATMOSPHERE ALONG AT LEAST A MAJOR PART OF SAID CHANNEL, THE IMPROVEMENT COMPRISING GUIDE MEANS ARRANGED IN SAID CHANNEL AND INCLUDING AT LEAST ONE GUIDE MEMBER WHICH CURVES FROM THE INTERIOR TO THE EXTERIOR OF SAID CHANNEL FOR DIRECTING THE GASES OUT OF THE CHANNEL. 